The overall aim of this project is to greatly improve the accuracy of the fluoro-deoxy-glucose (FDG) method of measurement of local cerebral metabolic rate of glucose (LCMRG) in ischemic brain tissue. Studies by Hawkins et al [6] have shown that when the existing FDG method is applied to ischemic tissue the resulting estimates and on the average, about 50% too low. The investigators have developed modifications of the data collection and analysis of the FDG method and performed statistical simulation studies to evaluate the relative accuracy of the new modified method, which is called Bayes Regression. These simulation studies indicate that the new modified method produces greatly improved relative accuracy in ischemic tisue: only 1 or 2% error. However this finding has not yet been validated in human stroke patients, and the main aim of this proposal is to obtain this validation. The secondary aims include the evaluation of other procedures proposed by others or by the investigators. The data used by Hawkins et al [6] mentioned above are available for analysis by Bayes Regression in this project. These data were obtained in the ischemic and contralateral normal regions of human stroke patients by repeated positron emission tomography(PET) scans for a period of 2 to 3 hours. The existing method used for routine clinical studies uses only a single PET scan taken at about 1 hour post-injection. While a data collection period of 2 to 3 hours is not practical for routine clinical studies, it does allow for computation of LCMRG by the "Direct" method which is known to produce accurate estimates of rate constants. A data collection period of 1 hour is practical for routine clinical studies; this collection period was used by Bayes Regression in the simulation studies, and only the first 1 hour's data from the stroke patients will be used in this project to validate the accuracy of Bayes Regression in ischemic tissue. The relative accuracy of LCMRG estimates by Bayes Regression will be assessed by comparison with estimates from the Direct method.